Two men, reportedly masked and dressed entirely in black, gunned down a Kaufman County, Texas, prosecutor this morning as he walked to a city courthouse. The Dallas Morning News reported that the victim had been “heavily involved” in the investigation of members of the Aryan Brotherhood.

The entire area was locked down and a search continued this afternoon for the two men who were described as having fled in a silver older model Ford Taurus. Meanwhile, KHOU-TV in Houston reported that the slain prosecutor was Assistant District Attorney Mark Hasse, a man who was said to be widely respected among jurists.

County Judge Bruce Wood said that courthouse security in Kaufman, a North Texas town of about 6,700 people about 30 miles southeast of Dallas, was always tight but not in the parking lot where Hasse was killed, WFAA-TV reported. Wood described the attack on Hasse as an “ambush,” the Dallas television station said.

The Aryan Brotherhood (AB) is a large, white supremacist prison gang that is infamous for its violence and its sprawling criminal empire, which also is highly active outside the nation’s prisons. A related group, the Aryan Brotherhood of Texas (ABT), is known to be particularly violent, and prosecutors in that state have been aggressively moving against its members for several years now.

Last November, the U.S. Department of Justice unsealed a 43-page indictment of 34 ABT members, accusing them of murders, attempted murders, conspiracies, arsons, assaults, robberies and drug trafficking. Ten could face the death penalty if convicted. A federal official said at the time that the gang's hallmark was the use of "extreme violence and threats of violence to maintain internal discipline and retaliate against those believed to be cooperating with law enforcement.

The AB was originally formed in 1964 at San Quentin Maximum Security Prison in San Quentin, Calif., as a response to the desegregation of the prison. It was initially a kind of racially based protective association for whites, but in the decades since then the AB has grown into the largest and most violent prison gang in America, with an estimated 15,000 members. Most members are in state or federal prisons, but an increasing number in recent years have helped to build up a criminal empire that is largely directed by AB bosses who are imprisoned, some of them serving life sentences.

Several years ago, the FBI said that while AB members make up less than one-tenth of 1% of the national prison population, they were responsible for 18% of all prison murders.

In 2005, federal officials in California indicted 40 AB leaders and associates from around the country and charged them with a series of murders and other crimes. Although many of those indicted were already serving life sentences, some of them in solitary confinement, prosecutors said they were still managing to have people killed and running criminal enterprises, typically sending messages through their wives or girlfriends, their lawyers and via secret codes and invisible ink. The idea of the case was to put many of those imprisoned leaders to death, as that seemed to be the only way of stopping them. In the end, the case largely failed, in that no AB member was sentenced to death.

What follows is a list of crimes or alleged crimes attributed to apparent ABT members culled from earlier Southern Poverty Law Center reports (with thanks to Hatewatch staffers Janet Smith and Don Terry):

October 2001: In the backlash against Arab-Americans that followed the Sept. 11 terrorist attacks, a Bangladeshi immigrant was gunned down while working at a Texas gas station. Mark Stroman, later convicted of the killing, was an ex-convict member of the Aryan Brotherhood (ABT) of Texas.

April 2002: Five members of ABT were arrested after a botched hit on another member resulted in an eruption of semi-automatic gunfire in a quiet Austin neighborhood. One of those arrested, ex-convict William Maynard, 31, was one of five "generals" who allegedly led the national Aryan Brotherhood. The FBI said the incident was part of a gang power struggle that had included a "string of killings" across the state.

June 2006: Three AB members allegedly stabbed to death a longshoreman in Baytown, Texas, because they wanted parts from his 14-year-old truck for a gang leader's vehicle. In ensuing days, the three were arrested and charged with capital murder. Police also arrested eight other alleged members or associates of the gang and charged them with engaging in organized crime.

December 2007: Dale Clayton Jameton, a ranking official of AB prison gang, pleaded guilty to the 2006 murders of a man in Mesquite, Texas, and an unnamed woman whose body has never been found. Officials say Anthony Clark was killed because he was suspected of informing, and the woman was murdered for reasons of "internal discipline." Jameton was sentenced to life without parole.

October 2009: A San Antonio, Texas, judge sentenced AB member Michael McCallum to 18 years in prison for beating to death a man he met at a gas station after the two had an argument about membership in white supremacist prison gangs. Security was heightened during McCallum's trial after a swastika was discovered on a prosecutor's car window.

October 2010: The most infamous racially motivated murder since the civil rights era occurred in 1998, when three white men, two of them ex-cons, tied a black man, James Byrd Jr., to the back of their pickup truck with a logging chain, dragged him to death over three miles of country roads outside Jasper, Texas, and then deposited his shredded remains in front of a predominantly black cemetery. One of the ex-cons testified at his trial that he and one his accomplices had both joined the ABT for protection from black inmates while they were incarcerated. When he rejoined society, his arms were covered with Aryan Brotherhood tattoos, including one depicting a black man being lynched. "You look at his arms," the trial prosecutor said, "and you see what's in his heart."

May 2011: AB member, Brent Stalsby, 30, of Beaumont, Texas, was sentenced to life in federal prison after pleading guilty to committing a violent crime in aid of racketeering activity for murdering a fellow member of the white supremacist gang and his girlfriend in 2007 on the orders of Carl Carver, a leader in the group. Charles Cameron Frazier, 29, was sentenced on June 21 to life in federal prison for his role in the murders and on June 28 Carver was sentenced to life in prison for ordering the murders.

September 2011: Steven Scott Cantrell, 25, of Midland, Texas, pleaded guilty to federal hate crime charges for setting fire to a predominantly black church in December 2010 in an effort to kill a disabled black man he believed lived at the church. The arson was part of a series of racially motivated arsons Cantrell committed in an attempt to gains status with the Aryan Brotherhood of Texas.

November 2012: In one of the largest racketeering cases of the year, the U.S. Department of Justice unsealed a 43-page indictment of 34 members of the “violent, whites-only prison-based gang with thousands of members operating” in and out of prisons throughout Texas and elsewhere. ABT was accused of carrying out murders, attempted murders, conspiracies, arsons, assaults, robberies and drug trafficking as part of an enterprise that goes back to at least 1993. Among those charged in the indictment were four senior leaders or “generals” — Terry Ross “Big Terry” Blake, 55; Larry Max “Slick” Bryan, 51; William David “Baby Huey” Maynard, 42, and Charles Lee “Jive” Roberts, 68.